SRv6 uSID: fundamental transformation of the IP stack#

Ahmed Abdeslam — Cisco

• Why: uSID is now a Proposed Standard (RFC 9800) with real hyperscaler deployments, and the talk connects it directly to AI backend fabrics and DCI — the PM's datapath-internals and DC/WAN-interconnect interests. It is also the clearest signal that SRv6 is displacing VXLAN/SR-MPLS layering in new DC designs.
• What: A Cisco view of SRv6 uSID: the 128-bit destination address becomes an ordered list of uSID instructions (typically ≤6 fit in the DA, SRH available for ultra-scale TE), replacing per-domain shims (MPLS core, VXLAN DC, GTP mobility). Includes third-party evidence: Microsoft quotes on why SRv6 fits AI backends (source routing instead of ECMP, path enumeration for latency, coupling with the workload scheduler, source-side failure detection), a Nebius design replacing VXLAN-in-DC + SR-MPLS-in-metro with one end-to-end uSID design with stateless service insertion, and an Alibaba ultra-scale DCI deployment across China. Claims >85k Cisco routers shipped uSID-capable and SONiC mainline support (350+ PRs, 1600+ commits, contributors incl. Microsoft, Alibaba, Broadcom, NVIDIA).
• How: uSID instructions bind to underlay TE, overlay, or service chaining; L3VPN/GRT services carried via BGP RFC 9252; AI backends run static uSID fabric + SDN controller rather than distributed routing; AI DCI argument is that MPLS TE doesn't fit (no MPLS in SONiC or DC hardware, pervasive-deployment cost, breaks end-to-end model).
• Where applicable: The technology is standardized and multi-vendor, but this is a vendor talk with marketing framing ("fundamental transformation") and the deployment evidence is hyperscaler-specific (Microsoft, Alibaba, Nebius). For an operator, the transferable content is the architecture pattern — single protocol end-to-end, source-routed TE — not a drop-in design.